THURSDAY, Jan. 18, 2018 (HealthDay News) -- The number of American adults who smoke has decreased, but nearly 38 million still put their health at risk by using cigarettes, U.S. government data show.

Cigarette smoking rates among Americans 18 and older fell from nearly 21 percent in 2005 to 15.5 percent in 2016. Among those who have ever smoked cigarettes, the percentage who have quit rose from just under 51 percent to 59 percent during that time.

The largest increase in quitting was among adults 25 to 44 years old, according to the U.S. Centers for Disease Control and Prevention.

Despite the decline in cigarette smoking, however, nearly 38 million adults still smoked cigarettes every day or some days in 2016.

"The good news is that these data are consistent with the declines in adult cigarette smoking that we've seen for several decades," said Corinne Graffunder, director of the CDC's Office on Smoking and Health.

"These findings also show that more people are quitting, and those who continue to smoke are smoking less," she said in an agency news release.

The average number of cigarettes smoked a day by daily smokers decreased from about 17 cigarettes in 2005 to 14 in 2016, the CDC reported.

During that time, the proportion of daily smokers who smoked 20 to 29 cigarettes a day fell from nearly 35 percent to 28.4 percent. The proportion of those who smoked fewer than 10 cigarettes a day increased from 16.4 percent to 25 percent.

"The bad news is that cigarette smoking is not declining at the same rate among all population groups," said Brian King, deputy director for research translation in the CDC's Office on Smoking and Health.

"Addressing these disparities with evidence-based interventions is critical to continue the progress we've made in reducing the overall smoking rate," King said in the release.

Cigarette smoking kills more than 480,000 Americans each year and is the leading preventable cause of disease and death in the United States.